Protective coatings for combustion engine exhaust systems



March 14, 1961 E. E. BRYANT ErAL 2,975,072

PROTECTIVE coATINGs FOR coMBUsTIoN ENGINE EXHAUST SYSTEMS Filed Deo. 9, 1958 INVENTORS Eugene E. Bryant Carl Reiff MMT United States Patent() PROTECTIVE COATINGS FOR COMBUSTION ENGINE EXHAUST SYSTEMS Eugene E. Bryant, Beachwood Village, and Carl J. Reiff, vRocky River, Ohio, assignors to Ferro Corporation,

Cleveland, Ohio, a corporation of Ohio Filed Dec. 9, 1958, Ser. No. 779,095 s claims. (ci. 117-68) This invention relates generally to protective coatings and more particularly to protective coatings for combustion engine exhaust systems.

Essential qualities of combustion engine exhaust systems for passenger and cargo carrying vehicles are light weight, economy, compactness, and durability combined with maximum sound deadening efficiency.

For the most part, these characteristics are achieved in present day automotive mufllers and tail pipes with the exception of durability.

Since, in order to achieve the characteristics of economy, light weight and compactness, present day com- A bustion engine exhaust systems, particularly automotive muillers and tail pipes, are' fabricated of light gauge ferrous base metal, they quickly succumb to the chemical attack of highly corrosive products of combustion from the interior, and to weathering and severe abrasive attack on the exterior. ln the Northern sections of the United States especially, the exterior attack is made the more severe by virtue of exposure to concentrated salt spray arising from the use of rock salt on streets and highways to facilitate melting and removal of ice and snow.

While a number of corrosion resistant metallic coatings have been used for the purpose f reducing corrosive attack, they are quickly broken through on the exterior by the abrasive action of highway grit and dust exposing the ferrous base metal alloy, thereby enabling chemical corrosion to set in at the points of abrasive attack through weathering and salt spray.

While a continuous porcelain enamel coating on the interior and exterior of automotive mufers and tail pipes would be adequate protection, the design of mufflers makes it virtually impossible to achieve an even coating of enamel throughout the interior. The nonuniform interior coating gives rise to localized points of attack by combustion gases inside the muffler at those points which the enamel has not completely covered. Furthermore in the fusion step, vitreous enamel on the interior tends to clog the ports and baffles inside the muler.

It is therefore an object of this invention to provide improved combustion exhaust systems having superior resistance to weathering and chemical attack.

It is further an object of this invention to provide a method for coating automotive mufers, tail pipes and the like in order to materially lengthen their useful life and to minimize the dangersof carbon monoxide poisoning arising from defective automotive mul'llers and tail pipes.

Other objects of the present invention will become apparent from the following description, appended claims and the drawings in which:

Fig. l is a fragmentary perspective view` of an automobile exhaust system including `a muffler and pipes connected thereto which embody the present invention;

and

Fig. 2 is an enlarged fragmentary sectional view on a 2,975,072 Patented Mar. 14, 1961 ICC plane taken through the line indicated at 2-2 in Fig. l and at a right angle to the metal sheet.

We have found that improved mufers, tail pipes, and' other hollow metal parts used in exhaust systems of combustion engines can be made by nickel plating relatively clean ferrous metal mufller stainpings, preferably before assembly, applying an unfused porcelain enamel coating to the exterior of the parts and thereafter fusing the porcelain enamel on the exterior surface.

As seen in the drawings, Fig. l shows combustion engine exhaust system parts including an automobile muffler 2 and connecting pipes 3 and 4. The exhaust system having parts that are hollow in form and as seen in Fig. 2, have metal walls 5 of 28 gauge steel. The walls 5 have a coating 6 of fused porcelain enamel which is a ground coat type enamel and a relatively thin layer 7 of an oxidized nickel coating interposed between the steel wall and the porcelain enamel. According to the present invention, at the same time the porcelain enamel layer is fused, a uniform corrosion resistant oxide bearing layer 8 is formed on the interior of the hollow ferrous article. This interior layer is the oxidation product of a nickel coating on ferrous base metal which nickel coating is deposited by a well known nickel reduction method such as by electroless means.

Thus, we have found an efficient method for obtaining improved protection against abrasive and chemical corrosion both on the interior and exterior surfaces of combustion exhaust parts, such as automotive mufllers and tail pipes. The two different types of coating; namely, the interior oxidized iron-nickel coating and the exterior fused porcelain enamel coating each afford maximum coverage and optimum protection to the interior andvexterior surfaces of the muffler and tail pipe respectively.

The interior coating is achieved by plating the ferrous metal muffler stampings with a thin, open layer of nickel by the nickel reduction method, although any suitable plating means would suice, prior to assembly. Or, in the alternative the coating may be applied to sheet stock prior to blanking the muffler parts.

After assembly, the exterior of the exhaust system part is then coated with porcelain enamel and fired at conventional enameling temperatures which fuses the porcelain coating and at the same time partially oxidizes the plated interior of the mulller with a dense, tightly adhering layer of iron oxide, rich in metallic nickel.

It is well known that iron oxide is highly resistant to corrosion, but its structure, as normally formed on the surface of ferrous base metal, is so open, that moisture penetrates easily to the ferrous base metal beneath the oxide resulting in continued oxidation. In our invention, the iron oxide formed in combination with the nickel deposit is more dense than iron oxide formed on bare ferrous base metal, and so adheres tightly to the ferrous base metal so that penetration of harmful gases and vapors to the base metal is minimized. The outer enamel coatingV at the same time provides maximum protection to the .exterior surfacesV against both the attack of weather exposure and salt spray, as well as the abrasive effects of highway grit and dust. Y

In the following disclosure it is understood that, while the nickel reduction method as taught in U.S. Patent No. 2,532,283 is preferred, and has been used with greatest success, any method of suitably coating the exhausst system parts with nickel may be employed.

While it is well known in Ithe enameling art that nickel undereoatings are beneficial to the application of one cover coat enamel where ground coats are not used, such benefits in this particular invention are purely incidental as the enamel coating highly preferred inthis invention is of the conventional adherence oxide bearing type which does not require such nickel coating for promotion of adherence.

Furthermore, although simply coating the muffler with a light nickel layer as described above (omitting the enameling step), followed by a heat treatment similar to that encountered when the outer enamel coating is red, would afford a `degree of both exterior and interior protection, the resultant fired iron oxide-nickel coating would not be resistant enough to the exterior abrasive forces encountered in day to day use, as the enamel coating, to make its commercial use feasible.

The iron oxide-nickel coating for the interior, while not as corrosion resistant as an enamel coating, affords in-use protection which is surprisingly much greater apparently because of the more complete, uniform coverage that cannot practically be achieved by an interior enamel coating, which would leave isolated areas unprotected promoting failure through localized chemical attack.

Although most of our work has been with present day automotive mufers and tail pipes, it is to be understood that this invention would be applicable to the ferrous base metal exhaust systems of any type combustion engine such as turbine, free piston or jet, wherein the exhaust system would be subjected to the same or similar conditions as described herein.

Following then is an example of a preferred method of carrying out the invention and'it is to be understood that this is just one of the innumerable variations of the invention which may be employed without departing from the scope or intent of the invention.

EXAMPLE First, Athe unassembled ferrous exhaust system parts of 28 gauge thickness are thoroughly cleaned of shop and mill grease in an alkaline cleaner, followed by a rinse in hot water.

The above designated parts are then pickled in sulphuric acid. The concentration is 6% by weight of sulphuric acid solution at a temperature of 145 F.i5 for a total immersion time of lminutes. The acid treatment is followed by a cold water rinse.

Next, nickel is deposited on the mufer and tail pipe by the well known electroless method of application, such as described in U.S. Patent 2,532,283 wherein the bath contained 4 ounces-i025 ounce per gallon of single nickel salts (Ni2SO4-6H2O), one ouncei0-5 ounce sodium acetate per gallon, and gramsiS grams sodium hypophosphite per gallon. This bath was maintained at a temperature of 97"i3"k F. at a pH of 5.25i0-25 for a total immersion time of y6 minutes. Total application of nickel per square foot is 0.10 gram-0.01 gram.

Theparts are then thoroughly rinsed in hot water and dried.

The unassembled, nickeled parts are then assembled, and put through an alkaline cleaner, dried and enameled on the exterior using conventional enameling methods according to the following formulas.

Enamel mill addition Ingredient: Parts by weight Bureau of Standards heating resisting frit Calcined alumina 25 Enameling clay 10 Hydrous borax 1/2 Citric acid crystals 1,440 Water 50 Apply to'the exterior of the nickel coated, cleaned muler by spraying at an application of 1011 gm. per square foot dry weight.

The above ingredients are ball milled to a neness of 1 gm. residue on a 200 mesh screen from a 50 cc. sample.

In the above formulation, the frit has the following raw material composition:

Raw material formula, Bureau of Standards No. 1

Ingredients: v Parts by weight Feldspar 31.0 Powdered quartz 11.4 Dehydrated borax 37.1 Soda ash 5.9 Fluorspar 9.0 Soda niter 3.8 Cobalt oxide 0.5 NCkl OXde 0.4 Manganese dioxide 0.9

This frit is made by smelting at a temperature of 2250" F. to a molten glass from which a smooth, stonefree thread may be drawn. After a smooth thread is obtained, the molten glass is quenched in water and dried.

After dryingr the unfused enamel coating, the coated muffler is fired at 1560 F. in a suitable enameling furnace for a length of time suicient to permit the piece to soak at the peak temperature for about one minute.

After firing, the muffler is cooled and inspected.

It is to be understood that, in accordance with the provisions of the patent statutes, variations and modil cations of the specific devices herein shown and described may be made without departing from the spirit of the invention. We therefore claim:

1. In an automotive exhaust system having a hollow article with a ferrous base metal wall and an exterior coating of porcelain enamel over an electrolessly plated nickel layer, `the combination therewith of a layer disposed on the interior surfaces of said hollow article cornprising an iron-nickel oxidation product of a nickel coating plated by electroless means on the interior surfaces of said hollow article prior to enameling, said iron-nickel oxidation product layer formed simultaneously with the fusing of the exterior coating of porcelain enamel.

2. In an exhaust system for a combustion engine cornprising a hollow ferrous metal article having a wall with interior and exterior surfaces: (l) a uniform interior coating on said wall of an oxide containing material which is the oxidation product of an electrolessly plated nickel coating on ferrous base metal (2) an exterior coating of a fused porcelain enamel containing an adherence promoting oxide and (3) an electrolessly plated nickel layer interposed between said porcelain enamel layer and exterior surface of said ferrous metal wall.

3. In an exhaust system for a combination engine comprising a hollow ferrous metal article having a wall with interior and exterior surfaces: (l) a uniform interior layer on said wall of an oxide containing material which is the oxidation product of an electrolessly plated nickel coating on ferrous base metal and (2) an exterior coating of a fused porcelain enamel containing an adherence promoting oxide and (3) a relatively uniform layer interposed between said enamel layer and the exterior surface of the wall which is an oxidation product of a nickel coating on a ferrous base metal, said porcelain enamel coating being thicker than said nickel-containing layers.

4. In a combination exhaust system having a hollow article with a ferrous base metal wall previously nickel plated by electroless means on both interior and exterior surfaces, and with a fused vitreous coating containing adherence promoting oxides over the previously nickel plated exterior, the combination therewith of a layer covering all the interior surfaces of said wall comprising a nickel-enriched layer which is an oxidation product of said previously plated nickel formed simultaneously with fusing of the exterior vitreous coating.

5. A method of making a corrosion resistant metal article suitable for use in combustion engine exhaust systems comprising the steps of nickel plating by electroless means the exterior and interior of a relatively clean hol- 10W ferrous metal article, applying a coating of unfused porcelain enamel containing an adherence promoting oxide on the exterior surface only of the plated metal article, and thereafter firing said article to form a fused porcelain enamel layer on the exterior of said metal article and form a uniform corrosion resistant nickeloxide containing layer on the interior surface of Said metal article which nickel-oxide containing layer is the oxidation product of said electroless nickel plating.

References Cited in the file of this patent UNITED STATES PATENTS Niedringhaus July 19, 1898 Schmidt Aug. 6, 1907 Scott et al. Nov. 12, 1935 McGohan Dec. 14, 1937 Long Dec. 25, 1945 Martin May 3, 1949 Zademach Oct. 9, 1951 Calton Jan. 1, 1952 Sweo Jan. 1, 1952 Whitehouse May 29, 1956 

5. A METHOD OF MAKING A CORROSION RESISTANT METAL ARTICLE SUITABLE FOR USE IN COMBUSTION ENGINE EXHAUST SYSTEMS COMPRISING THE STEPS OF NICKEL PLATING BY ELECTROLESS MEANS THE EXTERIOR AND INTERIOR OF A RELATIVELY CLEAN HOLLOW FERROUS METAL ARTICLE, APPLYING A COATING OF UNFUSED PROCELAIN ENAMEL CONTAINING AN ADHERENCE PROMOTING OXIDE ON THE EXTERIOR SURFACE ONLY OF THE PLATED METAL ARTICLE, AND THEREAFTER FIRING SAID ARTICLE TO FORM A FUSED PORCELAIN ENAMEL LAYER ON THE EXTERIOR OF SAID METAL ARTICLE AND FORM A UNIFORM CORROSION RESISTANT NICKELOXIDE CONTAINING LAYER ON THE INTERIOR SURFACE OF SAID METAL ARTICLE WHICH NICKEL-OXIDE CONTAINING LAYER IN THE OXIDATION PRODUCT OF SAID ELECTROLESS NICKEL PLATING. 